* The masses involved are very small. The force of gravity is directly proportional to the product of the masses. So, the smaller the masses, the weaker the gravitational force.

* The distance between the objects is very large. The force of gravity is inversely proportional to the square of the distance between the centers of the objects. The farther apart the objects are, the weaker the gravitational force.

In other words, gravitational force is weakest between objects with very small masses that are very far apart.

Here are some examples:

* The gravitational force between two dust particles in space is extremely weak because they have very small masses.

* The gravitational force between the Earth and a distant star is very weak because the distance between them is vast.

It's important to note that even though gravitational force can be very weak, it's still present everywhere in the universe and plays a significant role in the movement of celestial objects.